The present invention relates to a loop holding mechanism for holding and engaging loop portions of yarns successively produced at opposite side edges of a multi-axial yarn structure being formed and a machine for forming a multi-axial yarn structure.
It has been proposed to provide a machine for producing multi-axial yarn structures in which warp yarns are supplied in a warp feed direction in the form of a warp sheet and in which a yarn transfer device is provided which subjects warp yarns to successive bias yarn forming steps in which each yarn is caused to move in a succession of lateral transfer steps in a first weft direction to move from a first bias yarn reversal position to a second bias yarn reversal position and then to move in a succession of return lateral transfer steps in the opposite direction from the second bias yarn reversal position to the first bias yarn reversal position thereby to form a non-woven bias yarn assembly comprising two superposed non-woven bias yarn sub-assemblies in which the bias yarns of one sub-assembly are inclined to the bias yarns of the other sub-assembly and in both of which the bias yarns are inclined to the warp feed direction and in which each bias yarn at each reversal position in proceeding from a transfer step in one direction to a transfer step in the opposite direction forms a bias yarn loop portion.
In publication EP 0263392-A2 there is disclosed a machine for forming a two dimensional tetra-axial woven yarn structure embodying warp yarns, weft yarns and a bias yarn assembly having two bias yarn sub-assemblies in which the bias yarns of each are inclined to the bias yarns of the other and to the warp and weft yarns. The machine includes a yarn transfer device for progressively transferring yarns fed to it to provide the sub-assemblies of oppositely inclined bias yarns and in one form of yarn structure produced, the bias yarn sub-assemblies are arranged between outer warp yarns and outer weft yarns and the warp yarns are woven with the weft yarns to hold the intermediate bias yarns in place in the fabric.
The weaving together of the outer warp yarns and outer weft yarns in the machine disclosed in EP 0263392-A2 serves to hold the intermediate bias yarns in place in the structure and tensions in the bias yarns arising from their displacement by the traversing device are adequately absorbed in the woven structure thus formed.
In WIPO publication No. WO92/14876 a method of forming a three-dimensional woven yarn structure is disclosed in which use is made of a yarn transfer device for transferring yarns in the weft direction to provide bias yarn arrays in which the yarns are inclined to the warp feed direction and in which the arrays of inclined bias yarns are woven into other arrays of yarns by selective shedding of the yarns and insertion of weft yarns to produce the three-dimensional structure.
Again, the weaving of the arrays of bias yarns with other arrays of yarns and the insertion of weft yarns in the method disclosed in WO92/14876 allows the tensions in the bias yarns to be absorbed.
In U.S. Pat. No. 5,137,058 there is disclosed a machine for forming a three-dimensional yarn structure embodying warp yarns, weft yarns and non-woven bias yarns which are held together by binding warp yarns which pass through the yarn structure between adjacent non-binding warp yarns. The machine includes a yarn transfer device for progressively transferring yarns fed to it to provide non-woven sub-assemblies of oppositely inclined bias yarns which are fed into a binding zone where they are held in place within the warp and weft yarn structure by the binding warp yarns. The binding warp yarns are held captive at the upper and lower faces of the yarn structure by weft yarns inserted at each face. In addition, the bias yarns of the bias yarn sub-assemblies are held in place at their yarn reversal positions along each edge of the structure being formed by an outer binding warp yarn which passes through the bias yarn loop portions formed at the yarn reversal positions.
While the machine disclosed in U.S. Pat. No. 5,137,058 produces a three-dimensional yarn structure in which the non-woven bias yarn sub-assemblies are held in place by the binding warp yarns which pass through the structure and by the outer binding warp yarns, the yarn structure produced by the machine would have a tendency to reduce in width as a result of the tensions built up in the bias yarns of the bias yarn sub-assemblies.
In WIPO publication WO94/16131 a method of forming a multi-axial yarn structure is disclosed in which the two non-woven bias yarn sub-assemblies are formed in a yarn transfer device in which each yarn is caused in a succession of lateral transfer steps to follow the yarn preceding it from one position to another position in a lateral transfer path extending in the weft direction until the yarn has moved from a first bias yarn reversal position to a second bias yarn reversal position and then in a succession of return lateral transfer steps in the opposite direction and along the same transfer path until the yarn arrives at the first yarn reversal position. The lateral transfer steps and the return transfer steps are then successively repeated. The need to provide for a supply of yarns to the device from a rotary supply such as a rotary creel as required in the machine of U.S. Pat. No. 5,137,058 is by this mode of yarn transfer in the transfer device obviated.
The yarn structures produced in the method disclosed in WO94/16131 includes the two bias yarn sub-assemblies formed by the yarn transfer device and additionally includes binding warp yarns which pass through the bias yarn sub-assemblies and which are held captive at the lower or upper face or at the lower and upper faces of the yarn structure by insertion of weft yarns.
While the yarn transfer device disclosed in WO94/16131 has the advantage that it obviates the need for a rotary yarn supply, for example in the form of a rotary annular creel, there remains the disadvantage that the binding warp yarns which serve to hold the yarns of the bias yarn sub-assemblies in place in the structure may not in some circumstances adequately prevent the yarn structure being formed from reducing in width under the tensions developed in the bias yarns of the two bias yarn sub-assemblies.
In European patent publication No. 0573132-A1 there is disclosed a machine for producing a three-dimensional woven yarn structure in which weft yarns are arranged in columns which extend from one face of the structure to an opposite face and are interlocked by warp yarns which extend through the structure from a first of the two faces of the structure along an inclined path to the opposite face of the structure and then along a return inclined path back to the first face of the structure to produce what is known as an angle interlock woven yarn structure. In addition, selvedge forming warp yarns are woven into the structure so as to successively pass from one face to the other and back through the structure between adjacent columns of weft yarns.
In the machine disclosed in EP 0573132-A1 the yarn structure is described as being formed in the machine with the width direction of the structure extending vertically and with the inclined bias yarns and the selvedge forming warp yarns extending between upper and lower faces of the structure being formed. Selvedge holding mechanisms are described for engaging the loop portions of the selvedge forming warp yarns at the upper and lower faces of the yarn structure to prevent a reduction in the width of the woven structure being formed due to tension produced in the warp yarns and with the aim of maintaining the width (height) of the woven structure constant.
In a first of the selvedge holding mechanisms disclosed in EP 0573132-A1, there is provided an arrangement of four guide rails which extend in the direction in which the woven yarn structure is delivered from the weaving zone of the machine. Two of the guide rails extend along the length of the upper face of the woven structure at opposite upper edges of the structure and the other two guide rails extend along the length of the lower face of the structure also at opposite lower edges of the structure. Each of the rails provides for the support of a multiplicity of roller hook elements and a holding bar is passed through each loop portion of the selvedge forming warp yarn at each of the upper and lower faces of the woven structure, where it is hooked at each end on hooks of the roller hook elements which are caused to enter into and engage in the two guide rails at that face. When the woven yarn structure reaches a discharge end of the selvedge holding mechanism the roller hook elements disengage from the guide rails and subsequently the holding bar which they have supported is removed manually or automatically from the loop portions of the selvedge forming warp yarns and then inserted manually or automatically into the loop portions of selvedge forming warp yarns at the entry end of the guide rails where roller hook elements are provided for supporting the bar.
In an alternative selvedge holding mechanism disclosed in EP 0573132-A2 the roller hook elements and the guide rails supporting them are replaced by pin blocks which are guided in guide rails and which carry pins which are arranged to engage in the loop portions of the selvedge forming warp yarns at the upper and lower faces of the yarn structure being formed. There is however no disclosure as to how the pins are brought into engagement with the loop portions and as to how they are fed into the entry ends of the guide rails, removed from the exit ends of the rails and then returned to the entry ends of the rails and the pins again engaged in further loop portions of the selvedge forming warp yarn.
While the selvedge holding mechanisms disclosed in EP 0573132-A1 provide a means by which the woven structure being formed can be prevented from reducing in width, there is no disclosure of a means by which this can be achieved automatically and with a precision necessary for the reliable production of non-woven and partially non-woven multi-axial yarn structures.